Samsung & Sony LCD replacement won’t stick

I am doing a lot of LCD replacements on phones primary iPhones but also all different brands.

But I am a bit frustrated over Samsung & Sony, I can’t get the tom stick properly, they almost always loosen in top. I try to use the pre glued LCDs that have a frame to get a better result but they are a lot more expensive in the newer models (S6, S7).

I have done like others suggest on forums but I can’t get it perfect, are there any experts that can give me some light on what I am missing?

This is how I do it:

I clean the frame properly with IPA, then I use pre cut adhesive for the model and apply heat on the glass and put it in pressure for a couple of hours. But it tends to loosen in top a few hours after the pressure is released.